一个SQL语句

PCMB025H的唯一索引是coil_no,last_prod_date,要求选取coil_no唯一的资料，并且多笔coil_no相同的资料中取last_prod_date最大的一笔
		PCMB025H					查询结果
	coil_no	last_prod_date	coil_weight			coil_no	last_prod_date	coil_weight
	a	20090211	100			b	20090213	110
	b	20090213	110			a	20090213	90
	a	20090213	90			c	20090213	120
	c	20090213	120			d	20090213	95
	d	20090211	100
	d	20090213	95
	第一种： (select a.coil_no,a.last_prod_date,b.coil_weight from  (select coil_no,max(last_prod_date) last_prod_date from pcmb025h  group by coil_no having count(coil_no)>1) a  inner join  (select * from pcmb025h) b  on a.coil_no=b.coil_no and a.last_prod_date=b.last_prod_date)  union  (select * from pcmb025h where coil_no in  (select coil_no from pcmb025h group by coil_no having count(*) = 1)  ) 第二种： SELECT b.coil_no,b.last_prod_date,a.coil_weight FROM (SELECT * FROM pcmb025h) a, (SELECT coil_no,MAX(last_prod_date) AS last_prod_date   FROM pcmb025h p GROUP BY p.coil_no) b WHERE a.coil_no=b.coil_no AND a.last_prod_date=b.last_prod_date